1 files changed, 127 insertions, 0 deletions
diff --git a/trace2/tr2_sysenv.c b/trace2/tr2_sysenv.c
new file mode 100644
index 000000000000..5958cfc424b5
--- /dev/null
+++ b/trace2/tr2_sysenv.c
@@ -0,0 +1,127 @@
+#include "cache.h"
+#include "config.h"
+#include "dir.h"
+#include "tr2_sysenv.h"
+
+/*
+ * Each entry represents a trace2 setting.
+ * See Documentation/technical/api-trace2.txt
+ */
+struct tr2_sysenv_entry {
+	const char *env_var_name;
+	const char *git_config_name;
+
+	char *value;
+	unsigned int getenv_called : 1;
+};
+
+/*
+ * This table must match "enum tr2_sysenv_variable" in tr2_sysenv.h.
+ *
+ * The strings in this table are constant and must match the published
+ * config and environment variable names as described in the documentation.
+ *
+ * We do not define entries for the GIT_TRACE2_PARENT_* environment
+ * variables because they are transient and used to pass information
+ * from parent to child git processes, rather than settings.
+ */
+/* clang-format off */
+static struct tr2_sysenv_entry tr2_sysenv_settings[] = {
+	[TR2_SYSENV_CFG_PARAM]     = { "GIT_TRACE2_CONFIG_PARAMS",
+				       "trace2.configparams" },
+
+	[TR2_SYSENV_DST_DEBUG]     = { "GIT_TRACE2_DST_DEBUG",
+				       "trace2.destinationdebug" },
+
+	[TR2_SYSENV_NORMAL]        = { "GIT_TRACE2",
+				       "trace2.normaltarget" },
+	[TR2_SYSENV_NORMAL_BRIEF]  = { "GIT_TRACE2_BRIEF",
+				       "trace2.normalbrief" },
+
+	[TR2_SYSENV_EVENT]         = { "GIT_TRACE2_EVENT",
+				       "trace2.eventtarget" },
+	[TR2_SYSENV_EVENT_BRIEF]   = { "GIT_TRACE2_EVENT_BRIEF",
+				       "trace2.eventbrief" },
+	[TR2_SYSENV_EVENT_NESTING] = { "GIT_TRACE2_EVENT_NESTING",
+				       "trace2.eventnesting" },
+
+	[TR2_SYSENV_PERF]          = { "GIT_TRACE2_PERF",
+				       "trace2.perftarget" },
+	[TR2_SYSENV_PERF_BRIEF]    = { "GIT_TRACE2_PERF_BRIEF",
+				       "trace2.perfbrief" },
+};
+/* clang-format on */
+
+static int tr2_sysenv_cb(const char *key, const char *value, void *d)
+{
+	int k;
+
+	if (!starts_with(key, "trace2."))
+		return 0;
+
+	for (k = 0; k < ARRAY_SIZE(tr2_sysenv_settings); k++) {
+		if (!strcmp(key, tr2_sysenv_settings[k].git_config_name)) {
+			free(tr2_sysenv_settings[k].value);
+			tr2_sysenv_settings[k].value = xstrdup(value);
+			return 0;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Load Trace2 settings from the system config (usually "/etc/gitconfig"
+ * unless we were built with a runtime-prefix).  These are intended to
+ * define the default values for Trace2 as requested by the administrator.
+ *
+ * Then override with the Trace2 settings from the global config.
+ */
+void tr2_sysenv_load(void)
+{
+	if (ARRAY_SIZE(tr2_sysenv_settings) != TR2_SYSENV_MUST_BE_LAST)
+		BUG("tr2_sysenv_settings size is wrong");
+
+	read_very_early_config(tr2_sysenv_cb, NULL);
+}
+
+/*
+ * Return the value for the requested Trace2 setting from these sources:
+ * the system config, the global config, and the environment.
+ */
+const char *tr2_sysenv_get(enum tr2_sysenv_variable var)
+{
+	if (var >= TR2_SYSENV_MUST_BE_LAST)
+		BUG("tr2_sysenv_get invalid var '%d'", var);
+
+	if (!tr2_sysenv_settings[var].getenv_called) {
+		const char *v = getenv(tr2_sysenv_settings[var].env_var_name);
+		if (v && *v) {
+			free(tr2_sysenv_settings[var].value);
+			tr2_sysenv_settings[var].value = xstrdup(v);
+		}
+		tr2_sysenv_settings[var].getenv_called = 1;
+	}
+
+	return tr2_sysenv_settings[var].value;
+}
+
+/*
+ * Return a friendly name for this setting that is suitable for printing
+ * in an error messages.
+ */
+const char *tr2_sysenv_display_name(enum tr2_sysenv_variable var)
+{
+	if (var >= TR2_SYSENV_MUST_BE_LAST)
+		BUG("tr2_sysenv_get invalid var '%d'", var);
+
+	return tr2_sysenv_settings[var].env_var_name;
+}
+
+void tr2_sysenv_release(void)
+{
+	int k;
+
+	for (k = 0; k < ARRAY_SIZE(tr2_sysenv_settings); k++)
+		free(tr2_sysenv_settings[k].value);
+}